1. Field of the Invention
The present invention is directed to a backing pad for a hand guided polishing or sanding tool, as well as hand guided polishing or sanding tools including the backing pad of the present invention.
2. Description of the Related Art
Backing pads are used for a hand guided polishing or sanding tool. The tool can be electrically or pneumatically actuated. The backing pads known in the related art have an essentially plate-like form and a trapezoid cross-section with a top surface, a bottom surface and a slanting circumferential surface resulting in the bottom surface being larger than the top surface. The backing pads are adapted to be fixedly connected to a moving mounting part of the tool at its top surface and to receive a polishing or sanding material on the bottom surface. The backing pads are often provided with a plurality of channels each extending essentially radially and essentially parallel to the top and bottom surfaces through at least part of the backing pad. The backing pad has a central recess located in the bottom surface and a plurality of holes having a longitudinal extension essentially perpendicular to the top and bottom surfaces through the backing pad and connecting an opening in the bottom surface with an opening in the top surface.
Further, electrically or pneumatically actuated hand guided polishing or sanding tools include a backing pad with a polishing or sanding material attached to a bottom surface of the backing pad. The polishing or sanding material attached to the bottom surface performs a rotary, an orbital, a roto-orbital or a random orbital actuating movement if the tool is actuated.
Backing pads of the above-mentioned kind are well-known in the prior art. The backing pads usually have a plate-like circular form and are fixedly connected with their top surface to a moving mounting part of the tool performing the actuating movement. The tool can be actuated electrically or pneumatically. The tool's mounting part and consequently also the backing pad connected thereto performs a rotary, an orbital, a roto-orbital or a random orbital actuating movement around an axis of rotation if the tool is turned on. The tool's mounting part is usually a tool shaft actuated by a motor (electric or pneumatic) of the tool directly or via a respective gear mechanism located between the motor shaft and the tool shaft. The tool's mounting part includes an attachment (e.g. a threaded bore or an engagement element) for connecting the backing pad thereto. A threaded bore can be connected to a corresponding threaded rod provided at the top surface of the backing pad. An engagement element can be inserted into a corresponding receiving opening provided at the top surface of the backing pad and fixedly connected thereto.
Backing pads of the above-identified kind are known, for example, from EP 2 551 056 A1. The known backing pads comprise a carrier layer made of a rigid material and forming the top surface of the backing pad. The rigid material can be a rigid plastic material (e.g. nylon) or metal or a combination of these or other rigid materials. Furthermore, the backing pad is provided with an adhesive layer forming the bottom surface of the backing pad and adapted for releasably connecting the polishing or sanding material to the bottom surface of the pad. The polishing material can comprise, for instance, foamed plastic material, fur, micro fibers or the like. The sanding or abrasive material can be a sanding paper, a sanding fabric or the like. The adhesive layer can comprise, for instance, part of a hook-and-loop-connection (Velcro®) or similar. Finally, the backing pad comprises an interface layer made of a resilient and/or flexible material (e.g. polyurethane foam) and located between the carrier layer and the adhesive layer. Usually the backing pad is manufactured by prefabricating each of the layers separately and attaching them to one another by a gluing process.
The tool can be provided with a dust aspiration system creating an air flow during operation of the motor directed away from the working surface towards a suction tube. The air flow is directed from the working surface through holes (or bores) and channels (or cavities) provided in the backing pad towards the suction tube thereby aspiring dust laden air and providing it to a dust collecting unit, for example in the form of a dust filter or a separate dust suction device (e.g. vacuum cleaner) connected to the tool's suction tube. While the channels usually extend essentially radially in respect to the axis of rotation of the backing pad (or slightly inclined in respect to the radial direction), the bores usually extend axially, that is parallel to the axis of rotation, or slightly inclined in respect to the axial direction. The aspiration system can comprise a shroud (or cap) covering the top surface of the backing pad or at least part of it, thereby providing for an efficient dust aspiration. The polishing or sanding material attached to the bottom surface of the backing pad can be provided with holes corresponding in size and/or position to the backing pad's holes in the bottom surface and/or can be perforated in order to allow aspiration of the dust laden air from the working surface through the polishing or sanding material.
Another example for a known backing pad is offered for sale by KWH Mirka Ltd. It has 150 mm diameter and is adapted for an orbital, roto-orbital or random orbital actuating movement of 5 mm. The known backing pad features a central recess as air inlet for air flow and for extracting dust away from the center of the backing pad by the tool's dust extraction system. This backing pad is adapted to work with Mirka's so-called “Net Sanding” dust extraction concept, which comprises a sanding material having a net-like support structure and a backing pad with a plurality of essentially radially extending channels and essentially axially extending bores for aspiring dust laden air from the working surface through the net-like structure. The sanding material consists of dense network of polyamide fabric threads forming the net-like structure onto which the abrasive grit is bonded. This open weave net structure allows the dust particles to pass through the sanding material into the bores and channels of the backing pad and further into the tool's suction tube. This is described in detail in WO 2014/131936 A1.
The holes provided in the known backing pads extend through the bottom layer and at least through part of the resilient interface layer. Although some of the holes may even extend through the rigid carrier layer and open into openings in the top surface, the holes do not necessarily all extend through the entire height of the backing pad. Two or more holes, whether extending through the entire height of the backing pad or not, may be interconnected by one or more conduits. The conduits provided in the backing pads can extend through the resilient interface layer or the rigid carrier layer. Some of the conduits may extend along the top surface of the backing pad, which is then covered by a deflection plate for hermetically closing or sealing off the conduits.
In the backing pad known from Mirka there are radially extending horizontal channels each interconnecting an opening located in the slanting circumferential surface of the backing pad with a central recess. These interconnecting channels do not cross or intersect at any point the holes extending essentially axially through at least part of the backing pad. The interconnecting channels provide for a direct connection of the air surrounding the circumferential outer surface of the backing pad with the central recess. This constellation leads to a certain air flow during operation and use of the tool. The air flow runs from the environment surrounding the slanting circumferential surface of the backing pad, through the radially extending channels into the center recess. The air is blown out of the recess and is drawn radially outwards between the bottom surface of the backing pad and the working surface of the workpiece to the openings of the various holes distributed on the bottom surface of the backing pad thereby gathering dust. The dust laden air enters the openings in the bottom surface, passes through the holes and conduits (not the channels interconnecting the openings in the circumferential surface with the central recess) and exits the holes through openings located in the top surface. The various dust laden air streams exiting the openings in the top surface are combined by the shroud or cap of the dust extraction system and conveyed to the suction tube and further to the dust collecting unit, like a dust filter or a separate dust suction device (vacuum cleaner) connected to the tool's suction tube. In this known backing pad the center recess serves for providing enough air to the working surface at the center of the backing pad for realizing the desired radially extending air flow on the working surface from the central recess to the openings of the various holes in the bottom surface of the backing pad.
One disadvantage of the known backing pad is the fact that there are no holes near the outer circumference of the bottom surface and therefore, the dust extraction effect on the working surface is rather weak at the outer circumference of the backing pad and not very effective. In particular, due to the centrifugal force of the rotating backing pad, the dust generated at the outer circumference of the bottom surface is blown into the environment and leads to a severe increase of the dust concentration in the environmental air. In the known backing pad the holes and channels are formed after manufacturing of the pad by a subsequent drilling process. Due to the material used for the known backing pad in the prior art, in particular for the interface layer made of a resilient and flexible plastic material, it is not possible to form the holes and channels during its manufacturing. Therefore, in the prior art drilling additional holes extending essentially axially through the backing pad at the outer circumference of the bottom surface of the backing pad would make these additional holes exit on the top through the slanting circumferential surface. However, the slanting circumferential surface is not covered by the shroud or cap of the dust extraction system. Hence, these additional holes would be useless in the sense that they could not be used for aspiring dust. Furthermore, with the known backing pads having an air flow along the working surface from the center recess to the external circumference of the bottom surface, most of the dust laden air will already have been aspired by the holes located on the way from the center recess to the external circumference of the bottom surface. The air flow arriving at the external circumference of the bottom surface is very weak. So in the known backing pads even if there were additional holes located near the external circumference of the bottom surface they would not have much effect in terms of reducing the contamination of the surrounding air with dust and other small particles.